This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 199 26 832.0, filed on Jun. 12, 1999, the entire disclosure of which is incorporated herein by reference.
The invention relates to a subsonic aircraft preferably having backswept wings, whereby the tips of the lifting wings are equipped with so-called winglets for reducing the induced flow resistance or drag during cruise flight and especially also for minimizing the dangers posed by wing tip vortices to aircraft is following an aircraft equipped with such winglets.
In order to achieve the desired reduction of the induced flow resistance or drag during cruise flight, various different fixed winglet forms, of which the arrangement cannot be adjusted or moved during flight, have become known in the art. For example, the following general type of winglets are known; winglets that are suggestive of end disks secured to the wing tips; simple or single winglet arrangements including only a single winglet or wing end directed upward or downward; double winglet arrangements having two winglets directed upward or downward; multiple winglet arrangements in which several winglets are generally arranged in a fan pattern; and loop-shaped winglets or so-called spiroids.
German Patent Laying-Open Publication 36 21 800 describes an aircraft including a fuselage and lifting wings secured thereto. In the known aircraft, one or more individual small wings or winglets are arranged on the wing tip of each lifting wing generally oriented in a direction pointing away from the fuselage. The individual winglets are tilted or pivoted about their lengthwise axis in such a manner so that they point downwardly in the direction of the nose of the lifting wing. The angle of attack or incidence of the individual winglets is adjustable. Furthermore, winglets that have an adjustable length and or that are tiltable or foldable toward the rear are also provided. This tiltability or foldability can be interpreted as a rearward sweep of the individual winglet to as much as 90xc2x0. In this context, an optimal reduction of the induced flow resistance can only be achieved at one particular operating condition or point of the aircraft, because the individual winglets are not rotatable about an axis extending parallel to the aircraft lengthwise axis. Furthermore, it is especially not possible to reduce the span width of the aircraft wings equipped with such winglets while the aircraft is parked at a ramp or jetway. As a further disadvantage or limitation, a reduction of the safety risk for following aircraft is achieved only in the reduction of the induced drag. Thus, such an arrangement of winglets provides a significantly lesser degree of reduction of such risk than an arrangement of widely spread winglets with optimal incidence angles and auxiliary surfaces.
German Patent Laying-Open Publication 32 42 584 and related U.S. Pat. No. 4,722,499 (Klug) disclose an arrangement of auxiliary surfaces on the wing tips of a lifting wing. More particularly, preferably two adjacent auxiliary surfaces extend outwardly in the direction of the span width, whereby these auxiliary surfaces can be subjected to a controlled rotation of their total surface or of a partial surface thereof so as to vary the effectiveness thereof. The auxiliary surfaces are rotatable about an axis that lies approximately in the plane of the profile chord of the lifting wing. The individual winglets are not torsionally warpable or twistable, or torsionally adjustable, which leads to a lower effectiveness than if the winglets were so torsionally twisted. Further, in this known arrangement it is not possible to form large counter vortices.
The above described disadvantages also apply to the high lift wing arrangement known from German Patent Laying-Open Document 2 149 956, in which the wing tip comprises two or more partial wings or winglets, which are tiltable about an axis running in the aircraft lengthwise direction. These partial wings or winglets can be adjusted into a tilted position in which they are displaced successively in a fan-like arrangement relative to each other, wherein the forwardmost partial wing is adjusted the furthest upward while the rearmost partial wing is adjusted the furthest downward.
Published British Patent Specification 1 584 348 discloses devices or arrangements for reducing flow resistance or drag. These known devices comprise winglets that are adjustable about an axis extending parallel to the aircraft lengthwise axis. Disadvantageously, the adjustment of the winglets is achieved only in a collective manner, namely all of the winglets must be adjusted together as a group, without the respective angles between individual ones of the winglets being adjustable. Therefore, it is not possible to provide a wider spreading of the winglets relative to each other, so that the reduction of the safety risk posed to following aircraft is very small or minimal without the provision of additional auxiliary surfaces.
Two significant problems have been crystallized or realized during the research and development of future high capacity aircraft. These two problems relate to issues other than the reduction of the induced flow resistance or drag. For one, it wherein the tips of the lifting wings are equipped with so-called winglets. Particularly according to the invention, a streamline shaped rotation body is arranged at the tip of each lifting wing, whereby each such rotation body comprises at least two rotatably supported rotation segments. Further according to the invention, a respective winglet is mounted on each respective rotation segment, and each rotation segment with its associated winglet is individually pivotable in a prescribed angular range relative to the aircraft horizontal plane, about an axis of the rotation body that is approximately parallel to the aircraft lengthwise axis. Here, xe2x80x9capproximately parallelxe2x80x9d means within such a range to be generally parallel to the longitudinal axis of the aircraft or to the relative wind airflow direction or to the chord line of the wing at the wing tip. More particularly, the winglet or winglets of each respective rotation segment is/are pivotable through an angular range to respective pivoting end positions with an angle of at least +90xc2x0 (vertical or perpendicularly upward relative to the horizontal plane of the aircraft) or of at least xe2x88x9290xc2x0 (vertical or perpendicularly downward relative to the horizontal plane of the aircraft), with the angular range spanning between these end positions.
In addition to being rotatable about the axis of the rotation body, each winglet is preferably arranged on the respective rotation segment with a fixed or variable sweepback angle as well as a variable angle of incidence relative to the airflow direction or relative wind. The rotation body preferably has an optimized aerodynamic streamline contour that can be generally has been determined that the wing span width of such aircraft cannot become ever larger at will. Rather, the maximum wing span width must be limited to 80 m, for example, even though a further demand for improving the glide ratio of such aircraft exists, which would be served by further increasing the wing span width. As a second problem, such large high capacity aircraft have further increased the significant risk posed to aircraft that follow after such a high capacity aircraft during take-off or landing and thereby fly into the wing tip vortex wake of the high capacity aircraft. As a result, there is a high demand for measures that will minimize the negative effects of such wing tip vortices generated at the wing tips of high capacity aircraft.
In view of the above, it is an object of the invention to provide measures on a subsonic aircraft that achieve a reduction of the induced flow resistance or drag, make it possible to fly with a greater wingspan width as compared to the wingspan of the aircraft during parking of the aircraft at a ramp or jetway, and simultaneously achieving a minimization of the risks of wing tip vortices posed to following aircraft during flight. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as are apparent from the present specification.
The above objects have been achieved according to the invention in a subsonic aircraft, preferably having backswept wings, regarded as a teardrop, torpedo, or bullet shape made up of the individual rotation segments, and preferably includes four of such rotation segments with four respective winglets for example. The adjustment of each winglet can be carried out individually and independently of the other winglets by relatively simple means, using any conventionally known actuators for rotating and tilting each winglet as required, as well as any conventionally known sensors for sensing the respective actual position of each individual winglet. The winglets may respectively be provided with trailing edge flaps. The possibility is provided that all winglets can be used as ailerons. The term xe2x80x9crotationxe2x80x9d as used herein to describe the motion of the rotation segments and winglets about the rotation axis does not require free 360xc2x0 rotation, but rather especially refers to a partial rotation or pivoting through less than 360xc2x0.
In view of the relatively simple, adaptable and flexibly configurable arrangement according to the invention, the present winglet arrangement can easily be retrofitted on existing aircraft, as well as being incorporated into new aircraft.